What is Forensic Botany?


  • Application of plant science to criminal and civil investigations
    • Palynology: study of pollen and spores
    • Dendrochronology: tree-ring dating
    • Diatom analysis: aquatic forensic evidence


  • Interdisciplinary field drawing from botany, ecology, law enforcement


  • Why Plants Matter in Forensics…
    • Provide evidence of movement, time, or location of crime
    • Complement DNA, fingerprints, and traditional evidence
    • Versatile, especially in outdoor scenes or missing person cases

Locard’s Exchange Principle

  • “Every contact leaves a trace” – foundational forensic concept


  • Botanical evidence at the scene: Plants, pollen, seeds, and soil samples found at a crime scene can be linked to a suspect if they are also found on the suspect’s clothing, shoes, or vehicle.


  • Botanical evidence on the suspect:Conversely, plant material from the crime scene might be found on a suspect, indicating their presence at the location


  • Establishing links: This exchange of botanical evidence can be crucial in linking a suspect to a crime scene or victim, especially when other forms of evidence are scarce.

Types of Botanical Evidence


  • Macroscopic: Leaves, twigs, seeds, fruits, bark, wood
    • Examples: Identifying a specific type of leaf found on a suspect’s clothing, analyzing plant material in a victim’s stomach to determine time of death, or presence of a plant species to link a suspect to a crime scene.


  • Microscopic: Pollen, spores, diatoms, plant hairs (trichomes)
    • Examples: dentifying the species of a pollen grain found on clothing or examining diatom assemblages to determine if a victim drowned in a specific body of water


  • Each type tells a different story – location, season, transfer


  • Macroscopic and microscopic analyses often complement each other, providing a more comprehensive understanding of the plant evidence

Types of Botanical Evidence

Botanical Evidence Basics: Macroscopic

  • Look for unusual plant fragments at crime scenes - injuries (broken branches), or foreign species
    • can links suspects with crime scenes
    • experimenting with how long leaves on a broken branch take to wilt = timing


  • Use ecology (flowering times, growth cycles etc.) of plants growing in/around body
    • can determine timing of death (e.g. season)


  • Plant identification can be crucial for determining if poisoning has occurred
    • stomach contents, surrounding plants


  • Seeds, burrs, and plant fragments adhere to shoes, tires, hair can reconstruct movement of people, vehicles, or bodies

Botanical Evidence Basics: Palynology

  • Pollen & Spores - Pollen is unique by species, geographically distinct, and resists decay
    • can be carried by wind, water, or animals, traveling far from their source
    • individual grains of pollen from different species can look like soccer balls, sponges, padded cushions, or coffee beans
    • surfaces are covered with intricate identifiable geometric patterns



  • By examining pollen found at a crime scene or on a suspect, investigators can:
    • potentially link individuals or objects to specific locations
    • determine the time of year a crime occurred
    • reconstruct events related to the crime

Palynology in Drug Trafficking

  • In two different marijuana seizures in California and Texas, pollen analysis revealed a unique sagebrush pollen marker
    • sagebrush species was known to grow in only a few isolated regions of Mexico + pinpointed the likely area where the marijuana was cultivated


  • A truck carrying cocaine was seized at the Canadian border after attempting to enter from Detroit. Pollen analysis of the truck’s air filter revealed a pattern of pollen grains indicating the shipment originated in California and took a circuitous route across the United States instead of a direct path to Canada


  • Pollen analysis also has helped CBP trace the routes of marijuana and cocaine bundles that wash up onshore along the coasts of Florida and Texas
    • samples were loaded with fern spores, more than would be typical of an area where fern plants grow
    • There are only a few areas that have that many ferns and one of them is Fern Gully, a winding, scenic stretch of road in Jamaica

Botanical Evidence Basics: Diatoms and Aquatic Evidence


  • Diatoms are microscopic organisms that can be inhaled with water into the lungs
    • If the individual was alive when they entered the water, diatoms will be found in the lungs and may circulate to other organs
    • If the person was already dead, diatoms are less likely to be found


  • Comparing the types and quantities of diatoms in a victim’s body with samples from potential drowning locations (like lakes, rivers, or oceans) can help establish where the drowning occurred


  • Diatoms can also be transferred to clothing, footwear, or other personal items, potentially linking a suspect to a crime scene or a specific water source

Botanical Evidence Basics: Dendrochronology & Growth Clues


  • Tree rings are used to date wood
    • determine the age of wooden objects found at a crime scene
    • growth over time around buried objects indicates timeline of burial
    • climate records support or dispute timeline claims


  • Certain plants bloom or fruit in predictable seasonal windows
    • presence of specific plant structures can narrow time of crime
    • ueful in matching or challenging suspect alibis

Botanical Evidence Basics: Plant-Based Toxins and Injuries

  • Plants can cause injury or death: - Ricin from castor bean - Digitalis from foxglove - Coniine from hemlock
    • Socrates who was sentenced to drink hemlock
    • Abraham Lincoln’s mother due to white snakeroot
    • Juan Ponce de León died after being wounded by an arrow poisoned with the manchineel tree’s sap


  • Plant toxins can be used to prove a crime, such as homicide or theft, or to establish the cause of death in poisoning cases


  • Forensic scientists use analytical techniques to identify and quantify plant toxins in biological samples (e.g., blood, urine, stomach contents)

Botanical Evidence Basics: Modern Technologies

  • Stable Isotope Analysis - Measuring ratios of isotopes (C, N, O) in plants reflects regional climate or water and soil composition +can identify the source of illicit drugs or trace the origins of plants involved


  • Example - Local climate controls stomatal openings. When stomata are forced to close (drought) they stop discriminating against heavy isotope (13C)
    • Samples become more enriched in 13C compared to same species in an different climate

Its Time For A………